ELT's are supposed to be watertight, and the Honeywell unit looks to be built like a tank (with I price tag to match I would guess
)
There are Lithium powered 406's in the tails of King Airs all over the world, sitting on the ramp from Phoenix, to Miami. I doubt the cabin of a 787 is a worse environment.
I don't know quite what to think anymore....
